Fire detector and extinguisher system

ABSTRACT

The system uses a plurality of light sensitive diodes, a plurality of relays, a timer and a plurality of solenoids to detect fire and to control the quantity and distribution of fire fighting substance used on the fire.

iJnited States Patent Teeters 51 .iuly31l,l973

FIRE DETECTOR AND EXTINGUISHER SYSTEM Inventor: Lloyd L. Teeters, Star Rt., Cordes U.S. Cl. 340/418, 340/228 S, 340/419 Int. Cl. G08b 19/00 Field of Search 340/418, 419, 222

References Cited UNITED STATES PATENTS 10/ 1951 Rofi'man 340/418 Primary Examiner--Thomas B. Habcckcr Attorney-Warren F. B. Lindsley [57] ABSTRACT The system uses a plurality of light sensitive diodes, a plurality of relays, a timer and a plurality of solenoids to detect fire and to control the quantity and distribution of fire fighting substance used on the fire.

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. I 1 mil V1 "7 FIRE DETECTOR AND EXTINGUISHER SYSTEM BACKGROUND OF THE INVENTION The present invention pertains to a fire detector and extinguisher system and more particularly to a system which is especially adapted for use in a mobile home or in a house.

Light and/or heat sensitive devices are widely used in industry to detect fires and to turn on sprinkling systems to quench the fire or to reduce the damage until the fire department arrives. In many of the sprinkling systems water is used as the fire fighting substance. The device which detects the fire causes an alarm to be sounded and causes one or more valves to be opened so that water sprays over an area near the fire. However, in many prior art systems the water must be shut off manually when the fire has been extinguished. When the fire occurs in a building in a remote area the water may cause extensive damage to the property be fore the supply can be turned off. What is needed is a fire detector and extinguisher system which can turn on the supply of water or other fire fighting substance when a fire is detected and turn off the supply when the fire has been extinguished.

In homes or other buildings pipes which carry the supply of fuel into the buildings are often damaged during a fire so that the fuel from the damgaged pipes causes the fire to spread and makes it more difficult to extinguish the fire.

What is needed is a fire detector and extinguisher system which shuts off the fuel supply when a fire is detested and turns on a source of fire fighting substances. When the fire has been extinguished it is desired that the source of fire fighting substance be turned off.

SUMMARY OF THE INVENTION The present invention overcomes the disadvantages of the prior art by providing a detector which turns off the fuel supply when a fire is detected and causes fire fighting substance to be sprayed into the area where the fire is detected. After a predetermined period of time the source of fire fighting substance is turned off. If the fire is still detected the source is turned on again. If the fire is not detected the source remains off. This invention is especially useful in a mobile home or other buildings where the quantity of fire fighting substance is limited and where it is desired that damage which may be caused by the fire fighting substance be kept to a minimum.

It is, therefore, an object of this invention to provide a new and improved fire detector and extinguishersystem.

Another object of this invention is to provide a fire detector and extinguisher system which is especially adapted for use in a mobile home or house.

A further object of this invention is to provide a fire detector and extinguisher system which delivers a fire fighting substance for a predetermined period of time when a fire is detected, then checks the results and delivers an additional quantity of firefighting substance if the fire is still detected.

Still another object of this invention is to provide a fire detector and extinguisher system which disconnects the source of fuel from the structure being protected and controls the quantity and distribution of fire fighting substance used in fighting afire.

The foregoing objects are achieved in the present invention by employing a plurality of light sensitive diodes, a plurality of relays, a timer and a plurality of solenoids to detect a fire and to shut off the fuel supply, all arranged in a predetermined manner. A fire fighting substance is sprayed on a selected area where the fire is detected. After a predetermined length of time the supply of fire fighting substance is shut off. The supply if turned on again only if the fire is detected again.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a cross-sectional view of a building using the present invention.

FIG. 2 illustrates one embodiment of the present invention.

FIG. 3 illustrates another embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1 there is shown a building 10 having rooms 11 and 12 containing the fire detector and extinguishing system. Rooms 11 and 12 contain a water heater 14 and furnace 15, respectively. Gas or other fuel is supplied through a fuel solenoid 17 to a pipe 18 which is connected to the heater and the fur nace. Carbon dioxide or other fire fighting substance is supplied through a second pipe 20 and control solenoids 21 and 22 to a plurality of sprinkler heads 24-27. Solenoid 21 controls the quantity of carbon dioxide to heads 24 and 25. Solenoid 22 controls the quantity of carbon dioxide to heads 26 and 27. A plurality of sensors such as light sensitive diodes 29-32 supply signals to a control panel 34 when a fire is detected in the building 10. The diodes 29 and 30, for example, may be connected in a parallel circuit and other diodes may be connected in parallel with these diodes. If desired only one diode may be used in each room. The signals from the diodes cause the control panel to provide voltages which cause the fuel solenoid to shut off the supply of fuel to the heater and furnace. Signals from diodes 29 and 30 cause the control panel to provide voltage which causes solenoid 21 to open a valve and causes sprinkler heads 24 and 25 to spray carbon dioxide on a fire in room 11. Solenoid 22 controls a valve which controls the flow of carbon dioxide to sprinkler heads 26 and 27 in room 12.

FIG. 2 shows a circuit which can be used by the control panel 34 tosense a fire in building 10 and to control the solenoid shown in FIG. 1. In FIG. 2'two diodes are shown for each of the rooms 11 and 12 of FIG. 1; however, the operation of the circuit will be the same if a greater or lesser number of diodes is used. The first detector 36 includes light sensitive diodes 29 and 30, resistors 39-4l,transistor 42 and a relay having a coil CR1 and first and secondpairs of normally open contacts CRlA and CRIB. The contacts are shown to the right of the detector 36. Detector 37 includes light sensitive diodes 31 and 32, relay coil CR2, transistor 43 andresistors 45-47. The relay of detector 37 includes coil CR2 and first and second pairs of normally open contacts CRZA and CRZB.

A third relay includes a coil CR3, first, second and third 'pairs of normally open contacts CR'SA, 'CR3B, CR3D and a pair of normally closed contacts C-R3C. A fourth relay includes coil CR4, first and second pairs of normally open contactsCR4'A and CR4B and a pair of normally closed contacts CR4C. A timer 49 includes a timing mechanism a coil TD] and a pair of normally closed contacts TDlA. A normally closed switch 57, a green bulb 52, a red bulb 53 and an alarm 54 are also shown. Alarm 54 may contain a deenergizing switch 54'.

The operation of the circuit of FIG. 2 will now be described. The light sensitive diodes have a high value of resistance between anode and cathode when no radiation from a fire falls on the diode. When radiation from a fire falls on the diode the resistance between the anode and the cathode has a low value so that current flows from anode to cathode. When there is no fire, diodes 29-32 have a high value so that current does not flow. When there is no current in the diodes there is no current between base and emitter of transistors 42 and 43. When there is no current between base and emitter of transistor 42 and 43 these transistors are rendered nonconductive so that no current flows in relay coils CR1 and CR3 and all relay contacts are as shown in FIG. 2. When the contacts are as shown in FIG. 2, a current flows from the 24 volt potential through contacts CR3 and green bulb 52 to ground, causing the green bulb to light, indicating that there is no fire.

When there is a fire in room 11 (FIG. 1), diode 29 and/or 30 has a low value of resistance so that a current I flows from terminal 56 through resistor 39, diode 29 and/or 30, through resistor 40, from base to emitter of transistor 42, rendering transistor 42 conductive. When transistor 42 is rendered conductive, a current I flows from terminal 56 through CR1, from collector to emitter of transistor 42. Current I, energizes relay CR1 so that contacts CRlA close and contacts CRIB close.

When contacts CRlA close, a current I, flows from terminal 56 through CRlA, TDlA and CR3 to ground. Current I energizes relay CR3 so that contacts CR3A, CR3B and CR3D close and CR3C open. When CR3C opens the green bulb is no longer energized. When CR3B closes a current I, flows from terminals 56 through CR3B, CR4C and coil CR4 to ground. Current I, energizes relay CR4 so that contacts CR4A close, CR4B close, and a fraction of a second later contacts CR4C open. A portion of the current through contacts CR3B also flows through contacts CRIB and solenoid 21, causing solenoid 21 to open a valve so that carbon dioxide flows from sprinkler heads 24 and 25 into room 11 of FIG. 1. The closing of contacts CR3B also applies 24 volts to the timer TD], causing the timer to start timing out the duration of time that the carbon dioxide will flow into room 11. When contact CR3A closes, the +24 volts from tenninal 56 is coupled to the fuel solenoid l7 and to coil CR4. The 24 volts energizes solenoid 17, causing solenoid 17 to close a valve to shut off the fuel supply to the building. The 24 volts applied to coil CR4 keeps relay CR4 energized when contacts CR4C are open. Contacts CR4B now provide 24 volts to the red bulb 53 and to alarm 54 so that audible and visual warnings are provided.

After the 24 volts has been applied to timer TDl for a predetermined period of time, TDl opens contacts TDlA so that relay CR3 is deenergized. When relay CR3 is deenergized, contacts CR3B open so that timer TDI and solenoid 21 are deenergized. Switch 57 remains closed so that relay CR4 and fuel solenois 17 are still energized. The fuel supply is still shut off and the red bulb and alarm are still energized. Switch 57 must be opened by pressing a push button to deenergize relay CR4 and fuel solenoid 17. Relay contacts CR3/l are closed during the time that contacts TDlA are closed so that relay CR3 will remain energized if contacts CRlA should open when the fire is partially extinguished. If the fire is still burning when the timer is deenergized, relay CRl will still be energized so that carbon dioxide will again be sprayed into room II as described above.

The operation of detector 37 is similar to the operation of detector 36. A fire in room 12 causes diode 31 and/or diode 32 to have a low value of resistance so that a current I-, flows from terminal 56 through resistor 45, diode 31 and/or diode 32, through resistor 46, and from base to emitter of transistor 43, rendering transistor 43 conductive. When transistor 43 is conductive, a

current I flows from terminal 56 through relay coil- CR2 and transistor 43 to ground. Current I, energizes relay CR2 so that contacts CR2A close and CR2B close. When contacts CR2A are closed relay CR3 is energized, causing contacts CR3B and CR3E to close and apply 24 volts to timer TDl. The closed contacts CR2B cause solenoid 22 to be energized so that carbon dioxide is sprayed from sprinkler heads 26 and 27 into room 12 of FIG. 1.

FIG. 3 illustrates another embodiment of the present invention using l 10 volts AC. to operate the timer, solenoids, alarm, bulbs and relays of a portion of the circuit. The operation of the circuit of FIG. 3 is the same as the operation of the circuit in FIG. 2. The timer, relays, light sensitive diodes, transistors and solenoids are standard items which can be readily purchased.

Latching circuits including relay CR3 are for functional purposes. The light sensitive diodes may act as a one-shot triggering system, but CR1 and CR2 relays must be closed for the duration of an operating cycle.

While the principles of the invention have now been made clear in an illustrative embodiment, there will be many obvious modifications of the structure, proportions, materials and components without departing from those principles. The appended claims are intended to cover any such modifications.

What is claimed is:

l. A fire detector and extinguisher system for use with a source of fuel and first and second fire extinguishers, said system comprising:

first and second light sensitive diodes, ach having an anode and a cathode;

first and second relays, each having a coil and first and second pairs of normally open contacts, said coil of said first relay being coupled to said first diode, said coil of said second relay being coupled to said second diode;

third and fourth relays, each having a coil and first and second pairs of normally open contacts and a third pair of normally closed contacts;

first and second reference potentials;

a timer having a coil and a pair of normally closed contacts, said first pair of contacts of said first, said second and said third relays each being connected between said first potential and a first contact of siad timer, said coil of said third relay being connected between said second potential and a second contact of said timer;

first, second and third solenoids each having first and second terminals, said first and said second solenoids each controlling the output of a corresponding one of said extinguishers, said third solenoid controlling said source of fuel,

switch having first and second terminals, said first terminal of said switch being connected to said first first and second transistors each having a base, a collector and an emitter, said emitters of said first and said second transistors being connected to said second potential, said coil of said first relay being conpotential, said first pair of contacts of said fourth 5 nected between said first potential and said collecrelay being connected between said second termitor of said first transistor, said coil of said second nal of said second terminal of said switch and a first relay being connected between said first potential terminal of said third solenoid, said second termiand Said Collector of Said Second tl'arlsisrol';

nal of said third solenoid being connected to said first, second, third and fourth resistors, Said first second potential, said coil of said fourth relay being 10 sistor being connected between said second p connected between i fi t d id Second tial and said cathode of said first diode, said anodes minals of said third solenoid, said third pair of conof i first and sarfi secorld diodes beirlg pl tacts of said fourth relay being connected between to said first Potential: said second s r "8 said first terminal of said third solenoid and a first connerfted betweerr cathrrde of sald first dlode end of Said coil of said timer a Second end of Said l5 and said base of said first transistor, said third resiscoil of said timer being connected to said second tor bel'ng connected befween second PoterItlal potential, said second solenoid and said second sad cafthode of Sam second F Said fourth pair of contacts of said second relay being serially f bemg Fonnccted bstween f of connected between said first and said second ends second dlode and Sand base of second of said coil of said timer, said first solenoid and said translstor; second pair of contacts of said first relay being serian f havmg, first and 'f termmals l fi ally connected between said first and said second term'nal f alarm blemg fonnected to P end of said coil of said timer, said second pair of i l sfzcond bu S i l g contacts of said third relay being connected bei aarmd g i connecte to Sal secon ea 0 tween said first potential and said first end of said secon u 5. A fire detector and extinguisher system for use coil of said timer, and f f l d f t d d first and second bulbs each having first and second s: o t an secon ex leads, said first leads of said first and said second guts Sal Sys i i f first and second light sensitive diodes each having an bulbs being connected to said second potential,

anode and a cathode; said third part of contacts of said third relay being first and second relays each having a coil and first connected between said first potential and said secand second pairs of normally open contacts, said ond lead of said first bulb, said second pair of conf l b l d r tacts of said fourth relay being connected between col 0 re emg coup e i Sal I t t l d d I d f id ode, said coil of said second relay being coupled to said birsibpo en la an sai secon ea 0 sa secsaid second diode;

2 2 d h t d d third and fourth relays each having a coil and first etler f extmguls er Sys em as 6 me and second pairs of normally open contacts and a m c mm 1 me u third pair of normally closed contacts;

first and second transistors each having a base, a colfirst and Second third and fourth reference potem lector and an emitter, said emitters of said first and 40 tials.

said second transistors being connected to said seca timer having a coil and a pair of normally closed ond Potenuali of said s relay bfzmg contacts, said first pair of contacts of said first, said nected between said first potential and said collecsecond and said third relays each being connected tor of said first transistor, said coil of said second between said first potential and a first Contact of relay connected Petween r Potenual said timer, said coil of said third relay being conand sald collector of 52nd secon? translsiori and nected between said second potential and a second first, second, third and fourth resistors, said first re- Contact f said timer;

sistor bsing connected betwes" i secorrd poten' first, second and third solenoids each having first and tial and said cathode of said first diode, said anodes second terminals, Said fi t and i Second sole. of Said first and Said second dlodes belrlg coupled 5O noids each controlling the output of acorrespondto said first Potential, said second rsslstor s ing one of said extinguishers, said third solenoid connected between said cathode of said first diode controlling i source f f l and said base of said first transistor, said third resisa switch having fi t and second terminals, Said fi t tor beirrg connected bstween said second Potemral 55 terminals of said switch being connected to said a d a Cathode Of Sald Second f Said fourth third potential, said first pair of contacts of said resrsror bemg connected between said cathode of fourth relay being connected between said second said second diode and Said ba of Said Second terminal of said switch and a first terminal of said transistor. third solenoid, said second terminal of said third 3. A fire detector and extinguisher system as defined l n id b i connected t id f rth mmi l in claim 1 including: said coil of said fourth relay being connected'bean alarm having first and second terminals, said first t e s id fi st d id cond t r in ls f S id terminal of said alarm being connected to said first third solenoid, said third pair of contacts of said lead of said second bulb, said second terminal of fourth relay being connected between said first tersaid alarm being connected to said second lead of minals of said third solenoid and a first end of said said second bulb. 4. A fire detector and extinguisher system as defined in claim 1 including:

coil of said timer, a second end of said coil of said timer being connected to said fourth potentiahsaid second solenoid and said second pair of contacts of said second relay being serially connected between said second diode and said base of said second said first and said second ends of said coil of said transistor.

timer, said first solenoid and said second pair of contacts of said first relay being serially connected between said first and said second end of said coil 7. A fires detector and extinguisher system as defined in claim 5 including:

an alarm having first and second terminals, said first of said timer, said second pair of contacts of said third relay being connected between said third potential and said first end of said coil of said timer; and

terminals of said alarm being connected to said first lead of said second bulb, said second terminal of said alarm being connected to said second lead of said second bulb.

first and second bulbs each having first and second 10 leads, said first leads of said first and said second bulbs being connected to said fourth potential, said 8. A fire detector and extinguisher system as defined in claim 5 including:

first and second transistors each having a base, a colthird pair of contacts of said third relay being connected between said third potential and said second lead of said first bulb, said second pair of contacts of said fourth relay being connected between said third potential and said second lead of said second bulb.

6. A fire detector and extinguisher system as defined in claim 5 including:

first and second transistors each having a base, coland said collector of said second transistor; first, second, third and fourth resistors, said first relector and an emitter, said emitters of said first and said second transistors being connected to said second potential, said coil of said first relay being consistor being connected between said second potential and said cathode of said first diode, said anodes of said first and said second diodes being coupled to said first potential, said second resistor being nected between said first potential and said collector of said first transistor, said coil of said second connefted f cathofie of Sa 1d t dlofie relay being connected bgtween Said first potential and said base of said first transistor, said third resisand said collector of said second transistors; and tor belflg connected be tween said second Potemlal first, second, third and fourth resistors, said first resad cafthode of sald second f said fourth sistor being connected between said second potenbemg Fonnected bFtween Said cfithode of tial and said cathode of said first diode, said anodes Sald dlode and Said base of Sald Second of said first and said second diodes being coupled transistor; to said first ot tial, aid Second i t b i an alarm having first and second terminals, said first connected between said cathode of said first diode terminal of a alarm being Connected to said first and said base of said first transistor, said third resislead of Said Second bulb, Said Second terminal of tor being connected between said second potential said alarm being connected to said second lead of and said cathode of said second diode, said fourth said second bulb. resistor being connected between said cathode of 

1. A fire detector and extinguisher system for use with a source of fuel and first and second fire extinguishers, said system comprising: first and second light sensitive diodes, ach having an anode and a cathode; first and second relays, each having a coil and first and second pairs of normally open contacts, said coil of said first relay being coupled to said first diode, said coil of said second relay being coupled to said second diode; third and fourth relays, each having a coil and first and second pairs of normally open contacts and a third pair of normally closed contacts; first and second reference potentials; a timer having a coil and a pair of normally closed contacts, said first pair of contacts of said first, said second and said third relays each being connected between said first potential and a first contact of siad timer, said coil of said third relay being connected between said second potential and a second contact of said timer; first, second and third solenoids each having first and second terminals, said first and said second solenoids each controlling the output of a corresponding one of said extinguishers, said third solenoid controlling said source of fuel, a switch having first and second terminals, said first terminal of said switch being connected to said first potential, said first pair of contacts of said fourth relay being connected between said second terminal of said second terminal of said switch and a first terminal of said third solenoid, said second terminal of said third solenoid being connected to said second potential, said coil of said fourth relay being connected between said first and said second terminals of said third solenoid, said third pair of contacts of said fourth relay being connected between said first terminal of said third solenoid and a first end of said coil of said timer, a second end of said coil of said timer being connected to said second potential, said second solenoid and said second pair of contacts of said second relay being serially connected between said first and said second ends of said coil of said timer, said first solenoid and said second pair of contacts of said first relay being serially connected between said first and said second end of said coil of said timer, said second pair of contacts of said third relay being connected between said first potential and said first end of said coil of said timer; and first and second bulbs each having first and second leads, said first leads of said first and said second bulbs being connected to said second potential, said third pair of contacts of said third relay being connected between said first potential and said second lead of said first bulb, said second pair of contacts of said fourth relay being connected between said first potential and said second lead of said second bulb.
 2. A fire detector and extinguisher system as defined in claim 1 including: first and second transistors each having a base, a collecTor and an emitter, said emitters of said first and said second transistors being connected to said second potential, said coil of said first relay being connected between said first potential and said collector of said first transistor, said coil of said second relay being connected between said first potential and said collector of said second transistor; and first, second, third and fourth resistors, said first resistor being connected between said second potential and said cathode of said first diode, said anodes of said first and said second diodes being coupled to said first potential, said second resistor being connected between said cathode of said first diode and said base of said first transistor, said third resistor being connected between said second potential and said cathode of said second diode, said fourth resistor being connected between said cathode of said second diode and said base of said second transistor.
 3. A fire detector and extinguisher system as defined in claim 1 including: an alarm having first and second terminals, said first terminal of said alarm being connected to said first lead of said second bulb, said second terminal of said alarm being connected to said second lead of said second bulb.
 4. A fire detector and extinguisher system as defined in claim 1 including: first and second transistors each having a base, a collector and an emitter, said emitters of said first and said second transistors being connected to said second potential, said coil of said first relay being connected between said first potential and said collector of said first transistor, said coil of said second relay being connected between said first potential and said collector of said second transistor; first, second, third and fourth resistors, said first resistor being connected between said second potential and said cathode of said first diode, said anodes of said first and said second diodes being coupled to said first potential, said second resistor being connected between said cathode of said first diode and said base of said first transistor, said third resistor being connected between said second potential and said cathode of said second diode, said fourth resistor being connected between said cathode of said second diode and said base of said second transistor; and an alarm having first and second terminals, said first terminal of said alarm being connected to said first lead of said second bulb, said second terminal of said alarm being connected to said second lead of said second bulb.
 5. A fire detector and extinguisher system for use with a source of fuel and first and second fire extinguishers, said system comprising: first and second light sensitive diodes each having an anode and a cathode; first and second relays each having a coil and first and second pairs of normally open contacts, said coil of said first relay being coupled to said first diode, said coil of said second relay being coupled to said second diode; third and fourth relays each having a coil and first and second pairs of normally open contacts and a third pair of normally closed contacts; first and second, third and fourth reference potentials; a timer having a coil and a pair of normally closed contacts, said first pair of contacts of said first, said second and said third relays each being connected between said first potential and a first contact of said timer, said coil of said third relay being connected between said second potential and a second contact of said timer; first, second and third solenoids each having first and second terminals, said first and said second solenoids each controlling the output of a corresponding one of said extinguishers, said third solenoid controlling said source of fuel, a switch having first and second terminals, said first terminals of said switch being connected to said third potential, said first pair of contacts of said fourth relay being connected between said second terminal of said switCh and a first terminal of said third solenoid, said second terminal of said third solenoid being connected to said fourth potential, said coil of said fourth relay being connected between said first and said second terminals of said third solenoid, said third pair of contacts of said fourth relay being connected between said first terminals of said third solenoid and a first end of said coil of said timer, a second end of said coil of said timer being connected to said fourth potential, said second solenoid and said second pair of contacts of said second relay being serially connected between said first and said second ends of said coil of said timer, said first solenoid and said second pair of contacts of said first relay being serially connected between said first and said second end of said coil of said timer, said second pair of contacts of said third relay being connected between said third potential and said first end of said coil of said timer; and first and second bulbs each having first and second leads, said first leads of said first and said second bulbs being connected to said fourth potential, said third pair of contacts of said third relay being connected between said third potential and said second lead of said first bulb, said second pair of contacts of said fourth relay being connected between said third potential and said second lead of said second bulb.
 6. A fire detector and extinguisher system as defined in claim 5 including: first and second transistors each having a base, collector and an emitter, said emitters of said first and said second transistors being connected to said second potential, said coil of said first relay being connected between said first potential and said collector of said first transistor, said coil of said second relay being connected between said first potential and said collector of said second transistors; and first, second, third and fourth resistors, said first resistor being connected between said second potential and said cathode of said first diode, said anodes of said first and said second diodes being coupled to said first potential, said second resistor being connected between said cathode of said first diode and said base of said first transistor, said third resistor being connected between said second potential and said cathode of said second diode, said fourth resistor being connected between said cathode of said second diode and said base of said second transistor.
 7. A fires detector and extinguisher system as defined in claim 5 including: an alarm having first and second terminals, said first terminals of said alarm being connected to said first lead of said second bulb, said second terminal of said alarm being connected to said second lead of said second bulb.
 8. A fire detector and extinguisher system as defined in claim 5 including: first and second transistors each having a base, a collector and an emitter, said emitters of said first and said second transistors being connected to said second potential, said coil of said first relay being connected between said first potential and said collector of said first transistor, said coil of said second relay being connected between said first potential and said collector of said second transistor; first, second, third and fourth resistors, said first resistor being connected between said second potential and said cathode of said first diode, said anodes of said first and said second diodes being coupled to said first potential, said second resistor being connected between said cathode of said first diode and said base of said first transistor, said third resistor being connected between said second potential and said cathode of said second diode, said fourth resistor being connected between said cathode of said second diode and said base of said second transistor; and an alarm having first and second terminals, said first terminal of said alarm being connected to said first lead of said second bulb, said second terminal of said Alarm being connected to said second lead of said second bulb. 